All types of rendering. It's such a complex field. It requires both advanced software and (sometimes) specialized hardware. And the topic itself is incredibly wide: ray tracing, 4DGS, classic rendering techniques. It's so cool to see how quickly the boundaries are shifting in this area (in a good way)

Steam engines are pretty cool.

All the ones YC is looking for, especially crypto.

While there are still some cool things being done no doubt, I think by and large we've reached the point of diminishing returns in technology where new technologies are just required to compensate for problems created by existing technologies or are required to keep the economic system going by creating prisoner's dilemma instances.

And most technology seems to be more and more large-scale technology that requires many layers of abstraction and industrial production, rather than cool stuff people do by themselves to make the world a better place.

I used to be excited about new tech but now I just see it as a lost cause.